Internet Protocol (IP) Multimedia System (IMS) networks can provide Voice over IP (VoIP) and video services over a fourth generation (4G) wireless network. A 4G wireless network is an Internet protocol (IP) wireless access network in which different advanced multimedia application services (e.g., voice over IP (VoIP) content, video content, etc.) are delivered over IP. Some service providers separate their IMS elements, as well as voice and video services, into an IMS core site, which has no access to the Internet.
The IMS core site can include IMS elements, such as a Presence Server (PS) and an Offline Charging Server (OCS). The PS can be responsible for tracking devices' presence once the devices perform an IMS registration. The presence and availability of any particular device can be shared with other devices, which have subscribed to receiving presence and availability information. The OCS can be responsible for receiving offline billing records, as well as tracking subscribers' voice and data usage information.